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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>log</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_412"> </a>NAME</h4><blockquote>log - natural logarithm function</blockquote><h4><a name = "tag_000_007_413"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="math.h.html">math.h</a>>double log(double <i>x</i>);</code></pre></blockquote><h4><a name = "tag_000_007_414"> </a>DESCRIPTION</h4><blockquote>The<i>log()</i>function computes the natural logarithm of<i>x,</i>log<sub><i>e</i></sub>(<i>x</i>).The value of<i>x</i>must be positive.<p>An application wishing to check for error situations should set<i>errno</i>to 0 before calling<i>log()</i>.If<i>errno</i>is non-zero on return, or the return value is NaN, an error has occurred.</blockquote><h4><a name = "tag_000_007_415"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>log()</i>returns the natural logarithm of<i>x</i>.<p>If<i>x</i>is NaN, NaN is returned and<i>errno</i>may be set to [EDOM].<p>If<i>x</i>is less than 0, -HUGE_VAL or NaN is returned, and<i>errno</i>is set to [EDOM].<p>If<i>x</i>is 0, -HUGE_VAL is returned and<i>errno</i>may be set to [ERANGE].</blockquote><h4><a name = "tag_000_007_416"> </a>ERRORS</h4><blockquote>The<i>log()</i>function will fail if:<dl compact><dt>[EDOM]<dd>The value of<i>x</i>is negative.</dl><p>The<i>log()</i>function may fail if:<dl compact><dt>[EDOM]<dd>The value of<i>x</i>is NaN.<dt>[ERANGE]<dd>The value of<i>x</i>is 0.</dl><p>No other errors will occur.</blockquote><h4><a name = "tag_000_007_417"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_418"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_419"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_420"> </a>SEE ALSO</h4><blockquote><i><a href="exp.html">exp()</a></i>,<i><a href="isnan.html">isnan()</a></i>,<i><a href="log10.html">log10()</a></i>,<i><a href="log1p.html">log1p()</a></i>,<i><a href="math.h.html"><math.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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